Oscilloscopes have typically used 8-bit analog-to-digital converters (ADC) as an optimal tradeoff between system bandwidth and noise. ADCs with more bits typically operate at lower sampling rates. An 8-bit digitizer offers 256 levels of resolution for a non-averaged ideal dynamic range of approximately 48 dB; however, there are numerous applications that require more than 48 dB of dynamic range.
There are a few specialized oscilloscopes that offer 12 or 16 bits of resolution at low sample rate and bandwidth to cover some applications that require more than 48 dB of dynamic range. Also, sampling oscilloscopes have higher bits of resolution but require equivalent time sampling as a tradeoff.
Oscilloscopes also insert noise into signals. For applications such as pulse amplitude modulation (PAM-4), where there are four signal levels and three eye openings on the vertical scales, the noise produced from the oscilloscope's digitizers can have major adverse effects on the resulting measurement.
Average mode and high resolution acquisition modes have been incorporated into oscilloscopes to provide more bits of vertical resolution and reduce noise. However, this also reduces both signal noise and oscilloscope noise if they are random with respect to the trigger position. The ideal would be to only reduce the oscilloscope noise. In addition, averaging does not lend itself to the major application of acquiring long records of random patterns and building eye diagrams and performing jitter measurements, which is one of the primary uses of an oscilloscope. The average mode requires multiple triggered acquisitions and a repetitive signal. The high resolution mode can be performed on a single acquisition but such a mode requires significant reduction of the sampling rate and non-aliased bandwidth.
Embodiments of the invention address these and other limitations in the prior art.